Field of the Invention
The invention relates to a catalyst body that has a number of passages through which a medium can flow in a preferred direction.
Catalysts are used, for example, to remove nitrogen oxides, hydrocarbons, carbon monoxide and/or dioxins from the flue gas of an incineration plant. Catalysts of this nature may be configured as honeycomb catalysts. In a honeycomb catalyst, it is usual to provide a catalyst body that is in honeycomb form and has a number of passages through which a liquid and/or a gas, such as for example the flue gas, can flow in a preferred direction.
A honeycomb catalyst of this nature may be provided for reducing or oxidizing pollutants. The honeycomb catalyst which is provided as a DeNO.sub.x catalyst, for example, uses the so-called selective catalytic reduction (SCR) process, with an addition of a reducing agent, to reduce nitrogen oxides (NO.sub.x) to nitrogen (N.sub.2) and water (H.sub.2 O). However, the honeycomb catalyst that is configured as a dioxin catalyst also has a certain SCR activity. For example, a dioxin catalyst oxidizes polychlorinated dibenzodioxins/dibenzofurans using molecular oxygen.
To catalytically clean the flue gas from stationary or mobile incineration plants or internal combustion engines, honeycomb catalysts are used, the catalyst bodies of which have a square passage geometry. German Patent DE 28 19 378 C2 discloses a honeycomb body with cells which are guided through and are of substantially rectangular basic shape. In this case, the longitudinal sides of a first group of the passages are disposed approximately at right angles to the longitudinal sides of a second group of the passages.
The number of channels may in this case be 10/6.452 cm.sup.2. Published, Non-Prosecuted German Patent Application DE 37 13 209 A1 also discloses a honeycomb body with passages of approximately rectangular cross section. A ceramic structure body with a honeycomb body whose passages are approximately rectangular in cross section is also known in principle from the reference titled "Haus der Technik (House of Technology", Prof. E. Steinmetz (Ed.), Vulkan-Verlag Essen, (1992), p. 23.
However, with catalyst bodies of this nature there is a risk of mechanical blockage of the honeycomb openings caused by flue dust. Therefore, regular, comparatively expensive cleaning of the catalyst is required in order to ensure that the catalyst operates reliably. In addition, the production of catalyst bodies of this nature involves the problem of cracking during the manufacturing process owing to the internal stress of the catalyst bodies.